1. Field of the Invention
The present invention relates to an emulsifier adapted for use in the process of emulsion polymerization of vinyl monomers. More specifically, the present invention provides a nonionic surfactant which can be used as an emulsifier in the emulsion polymerization reaction of vinyl monomers. The nonionic surfactant is prepared by adding 30 to 100 mols of an alkylene oxide to 1 mol of a polyhydric alcohol having 3 to 10 functional hydroxyl groups and then esterifying the resultant compound thereby to introduce 1 to 2 mols of an acyl group having 6 to 22 carbon atoms.
2. Description of the Prior Art
The emulsion polymerization process is of industrial utility for polymerizing vinyl monomers. Polymers prepared by means of the emulsion polymerization process include polyvinyl chloride, synthetic rubbers, polyacrylic acid esters, polymethacrylic acid esters, polyvinylidene chloride, polychloroprene and copolymers thereof. The aforementioned polymers can be recovered from the emulsions for use in the forms of moldable plastics or rubbers, or they can be used in the emulsified state for adhesives, paper processing, fiber processing or other general industrial uses.
Anionic surfactants, such as sulfates of long chain alcohols, alkylbenzene sulfonates and soaps, and nonionic surfactants, such as polyoxyethylenealkyl ethers, polyoxyethylenealkylphenyl ethers, polyoxyethylenesorbitan fatty acid esters or polyoxyethylene fatty acid esters, have been used as emulsifiers for emulsion polymerization, either singly or in mixtures of anionic and nonionic surfactants.
The particular emulsifier used in the emulsion polymerization process exerts significant influences not only on the initiation and propagation reactions in polymerization, but also on the stability of the polymerizing resin emulsion and further on the mechanical and chemical stabilities of the resultant resin emulsion and on the stability of the emulsion when it is frozen or stored.
In general, anionic surfactants have high emulsifying activity and the resin emulsions formed by the use of such anionic surfactants have superior mechanical stabilities. However, the anionic surfactants have disadvantages in that if polyvalent cations, such as calcium ions, aluminum ions, magnesium ions or barium ions, are admixed into the emulsion, insoluble salts are formed thereby to demulsify the system. Consequently, it is difficult to use an anionic surfactant as the emulsifier when the emulsified resin is put to use with the addition of a filler material such as an inorganic pigment or salts or oxides of various metals. It is preferable to use a nonionic surfactant in the latter case.
As will be understood from a consideration of their molecular structures, the nonionic surfactants are not as sensitive to various ions as are the ionic surfactants, and they have higher chemical stabilities than the ionic surfactants. However, a large amount of agglomerated products is formed during the polymerization reaction and the mechanical stability of the resultant resin emulsion is not satisfactory when polyoxyethylenealkyl ethers, polyoxyethylene fatty acid esters, or polyoxyethylenesorbitan fatty acid esters, are used as the emulsifier for emulsion polymerization. On the other hand, the amount of the agglomerated products formed is small and the resultant resin emulsion is superior in its mechanical and chemical stabilities when a polyoxyethylenealkylphenyl ether is used as the emulsifier for emulsion polymerization. For this reason, polyoxyethylenealkylphenyl ethers have been preferred for use as the emulsifiers for the emulsion polymerization of vinyl monomers.
However, in recent years waste water processing has become a serious problem and the oil content and the COD value of the waste water is strictly regulated. Polyoxyethylenealkylphenyl ethers, which have been conventionally used as emulsifiers for emulsion polymerization, have benzene nuclei in their lyophilic portions and they are extremely difficult to decompose by microbiological attack. In order to remove or recover the same from the waste water, large size equipment and great expense is required. Moreover, it is undesirable to flow non-decomposed alkylphenols into bodies of waters, such as lakes, rivers and seas, in view of their poisonous characters. For this reason, the use of nonylphenol has been discontinued in European countries. A new nonionic surfactant is required which can be used in place of the polyoxyethylenealkylphenol ethers.